Light scattering and distribution model for scintillation cameras

Light distribution in a standard scintillation camera is a complex process. The photons come across many different optical materials and many types of specular and rough optical surfaces. Complexity is further added to the model when the spatial and angular sensitivities of the detection components--the photomultipliers--are considered. To be able to correctly predict the PSF of a gamma camera, we developed a Monte-Carlo ray-tracing model which was subsequently compared to data measured on an existing gamma camera head (PRISM 3000 from Picker International Inc.). The experimental configuration was first replicated: geometry, optical properties of the crystal, light guide, photomultiplier tube window and photocathode, index matching fluid and gamma ray energy. Several other parameters, such as back mirror reflectivity and border reflectivity, were the optimized. Finally an a posteriori modelization of the scattered refracted and reflected fields at the rough interface between the crystal and the light guide was obtained by fitting simulation results to experimental data.